JP2011122228A - Method for operating blast furnace - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for operating a blast furnace which achieves, even under the condition of drastically reduced production, a stable operation without bringing about the cost-increase caused by increase in reducing material ratio. <P>SOLUTION: In the method for operating the blast furnace under the condition of the reduced production of ≤1.8 Nm<SP>3</SP>/(minxm<SP>3</SP>) being a bosh-gas ratio defined with a bosh-gas amount per 1m<SP>3</SP>of the inner volume in the blast furnace, the charging material distributing control and/or the adjustment of the blasting speed before tuyere, are performed so that a center gas flowing index defined with the furnace top-center gas temperature (°C)/the furnace top gas average temperature (°C) becomes 2.0-3.0 and a peripheral gas flowing index defined with the furnace peripheral gas temperature (°C)/the furnace top gas average temperature (°C) becomes 1.0-1.5. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a blast furnace operating method under reduced production operating conditions.

  When there is a sudden decline in steel demand due to changes in the economic situation, it may be necessary to continue production cuts in the blast furnace for a long time.

As means for reducing the production of a blast furnace, there are mainly two means: reduction of the amount of oxygen blown from the tuyere (reduction of enriched oxygen amount and / or blast amount) and increase of the reducing material ratio. However, when the production is reduced by reducing the amount of oxygen, the amount of Bosch gas decreases, the central gas flow cannot be maintained, and stable operation of the blast furnace cannot be secured, so the Bosch gas ratio (Bosch gas amount per 1 m ^{3 of} blast furnace volume) There was a limit of about 1.8 Nm ³ / (min · m ³ ), and further reduction in production required a reduction in the rate of charge drop due to an increase in the ratio of reducing materials.

  However, a reduction in production due to an increase in the reducing material ratio has a problem in that the manufacturing cost of the hot metal is increased, the Si concentration in the hot metal is increased, and the desiliconization cost in the subsequent process is increased.

  By the way, it is well known that securing a central gas flow is important for stable operation of a blast furnace during normal operation (not during production reduction). For example, when the present applicant performs coke center charging under the pellet multiple blending condition in which the pellet blending ratio in the ore is 50 mass% or more, the ore layer thickness ratio Lo / (Lc + Lo) at the uppermost part in the furnace is By setting the furnace center region (R / Ro ≦ 0.1) to 0.1 or less and the furnace peripheral region (0.6 ≦ R / Ro ≦ 1.0) to 0.5 or more, the central gas flow Ensuring stable gas flow in the furnace and maintaining good ventilation in the furnace, maintaining a high furnace top gas temperature, and zinc gas is discharged from the blast furnace along with the high temperature furnace top gas. Therefore, the blast furnace operating method which can suppress the adhesion of zinc to the furnace wall was developed (see Patent Document 1).

  However, when trying to apply the blast furnace operation method described in Patent Document 1 to a production reduction operation by reducing the amount of oxygen, the total amount of gas passing through the blast furnace (Bosch gas amount) decreases as the amount of oxygen decreases. If a large amount of gas is directed to the center of the furnace in order to secure the central gas flow, the amount of gas that can be directed to the periphery of the furnace is reduced. As a result, the ability of gas reduction (indirect reduction) to dissolve ore existing in the periphery of the furnace is reduced, causing rapid direct reduction (smelting reduction) at the lower part of the furnace, resulting in deterioration of the air permeability at the lower part of the furnace. As a result, fluctuations in the blast pressure increase and operational stability is lost, increasing the possibility of operational troubles such as shelf hanging, slipping, and blowout.

  Therefore, in order to perform a significant reduction in production beyond a certain level, it was necessary to adopt a reduction in production due to an increase in the ratio of reducing materials in addition to a reduction in the amount of oxygen, which forced a high-cost operation.

  In Patent Document 2, after charging the coke or ore charge into the blast furnace, the gas temperature at the top of the blast furnace is measured with a plurality of thermometers installed in the furnace radial direction at the top of the blast furnace, The measured gas temperature pattern in the furnace diameter direction at the top of the blast furnace furnace is compared with a preset gas temperature pattern to determine the charge distribution state of the charge in the furnace diameter direction of the blast furnace. A state determination method is disclosed. According to this method, the flow behavior of the charge charged into the blast furnace can be accurately obtained, and the blast furnace operation can be performed stably. Below, it is difficult to set the gas temperature pattern in advance, and it is not possible to solve the above-mentioned problems in a significant reduction in production.

JP 2008-184626 A JP 2006-265647 A

  Therefore, an object of the present invention is to provide a blast furnace operating method capable of realizing a stable operation without incurring an increase in cost due to an increase in the ratio of reducing materials even under a drastically reduced production operation condition.

The invention described in claim 1 is a blast furnace operating method under a reduced production operating condition in which a Bosch gas ratio defined by a Bosch gas amount per 1 m ^{3 of} blast furnace internal volume is 1.8 Nm ³ / (min · m ³ ) or less. The center gas flow index defined by the furnace top center gas temperature (° C.) / The furnace top gas average temperature (° C.) becomes 2.0 to 3.0, and the furnace top peripheral gas temperature (° C.) / Furnace top Blast furnace operating method characterized by performing charge distribution control and / or adjusting wind speed before tuyere so that ambient gas flow index defined by gas average temperature (° C) is 1.0 to 1.5 It is.

  The invention described in claim 2 is the blast furnace operating method according to claim 1, which is performed under a high pulverized coal ratio operating condition with a pulverized coal ratio of 150 kg / t-molten iron or more.

  Invention of Claim 3 is a blast furnace operating method of Claim 1 or 2 performed on the pellet multi-mixing operation conditions whose pellet mixing rate in an ore is 15 mass% or more.

  According to the present invention, the core gas flow index defined by the furnace top central gas temperature (° C.) / Furnace top gas average temperature (° C.) and the furnace top peripheral gas temperature (° C.) even under a production cut-off operation above a certain level. / By controlling the charge distribution so that the ambient gas flow index defined by the furnace top gas average temperature (° C) is within the specified range, the central gas flow can be reduced without increasing the reducing agent ratio. While maintaining the gas flow to the furnace periphery, it is possible to maintain the ability to gas reduce (indirect reduction) or dissolve the ore present in the furnace periphery. Operation stability can be ensured without causing fluctuations in pressure loss.

It is a transition figure showing change of a blast furnace operation result before and after application of the present invention. It is a graph which shows the relationship between a Bosch gas ratio and a center gas flow index. It is a graph which shows the relationship between a Bosch gas ratio and a surrounding gas flow index. It is a graph which shows the relationship between a Bosch gas ratio and ventilation pressure fluctuation | variation.

  Hereinafter, a case where the present invention is applied to the operation of a blast furnace having a bellless charging device using a turning chute will be described in more detail as a representative example.

Embodiment
The present invention relates to a blast furnace operating method under a reduced production operating condition in which the Bosch gas ratio defined by the amount of Bosch gas per 1 m ^{3 of} blast furnace volume is 1.8 Nm ³ / (min · m ³ ) or less, The central gas flow index defined by gas temperature (° C.) / Furnace top gas average temperature (° C.) is 2.0 to 3.0, and top gas temperature around the top (° C.) / Top gas average temperature (° C. The blast furnace operating method is characterized in that the charge distribution control is performed so that the peripheral gas flow index defined in (1) is 1.0 to 1.5.

As described above, the present invention is applied to blast furnace operation under reduced production operation conditions in which the Bosch gas ratio defined by the amount of Bosch gas per 1 m ^{3 of} blast furnace volume is 1.8 Nm ³ / (min · m ³ ) or less. .

The Bosch gas amount V _bosh (unit: Nm ³ / min) is calculated by the following formula (1).

V _bosh = V _N2 + V _H2 + 2V _O2 Formula (1)
Here, V _N2 : the amount of N ₂ charged from the tuyere (Nm ³ / min), V _H2 : the amount of H ₂ charged from the tuyere (Nm ³ / min), V _O2 : the amount of O ₂ charged from the tuyere (Nm 3 / ^min) at and, for example, when performing blowing pulverized coal, the total amount of each component contained in the pulverized in coal blowing.

Here, the Bosch gas ratio was limited to 1.8 Nm ³ / (min · m ³ ) or less when the Bosch gas ratio exceeded 1.8 Nm ³ / (min · m ³ ). The total amount of gas (Bosch gas flow rate) is sufficient, so even if a large amount of gas is directed to the center of the furnace to secure the central gas flow, a sufficient amount of gas may still be directed to the periphery of the furnace. This is because the operation stability can be maintained by the conventional charge distribution control without applying the present invention.

  The central gas flow index defined by the furnace top center gas temperature (° C.) / The furnace top gas average temperature (° C.) becomes 2.0 to 3.0, and the furnace top peripheral gas temperature (° C.) / Furnace top Charge distribution control is performed so that the peripheral gas flow index defined by the gas average temperature (° C.) is 1.0 to 1.5.

  Here, as the target index for charge distribution control, the center gas flow index defined by the furnace top center gas temperature (° C.) / The furnace top gas average temperature (° C.) and the furnace top peripheral gas temperature (° C.) / Furnace The reason why the peripheral gas flow index defined by the average top gas temperature (° C.) is used is as follows.

  That is, since the gas at the top of the furnace contains a large amount of dust, it is not practical to always directly measure the gas flow rate at the top of the furnace, so it is known to have a positive correlation with the gas flow rate at the top of the furnace. The furnace top gas temperature, which is easy to measure at all times, is used, and this is divided by the furnace top gas average temperature to make it dimensionless and used. For example, if the central gas flow index (or ambient gas flow index) exceeds 1.0, it means that the gas flow rate at the furnace center (or around the furnace) at the furnace top is greater than the average gas flow rate at the furnace top.

  Here, the furnace top center gas temperature and the furnace top peripheral gas temperature can be obtained from the furnace top gas temperature distribution measured by a plurality of thermometers installed in the furnace radial direction of the furnace top. As for the furnace center gas temperature, if a thermometer can be installed at the furnace center at the furnace top, the gas temperature measured with the thermometer may be used as the furnace center gas temperature as it is. If a thermometer cannot be installed at the center, the gas temperature at the furnace center may be estimated by an extrapolation method using the gas temperatures measured by two thermometers from the side closest to the furnace center. For example, two thermometers are installed from the side closest to the furnace center at positions a and b (a <b) from the furnace center, and the temperatures measured by these thermometers are T1 and T2, respectively. In this case, the furnace top center temperature Tc can be calculated by Tc = T1 + (T1−T2) / (b−a) × a. As for the gas temperature around the furnace top, if a thermometer can be installed close to the furnace wall, the gas temperature measured with the thermometer can be used as the gas temperature around the furnace top as it is, but it is close to the furnace wall. If the thermometer cannot be installed, the gas temperature measured by the two thermometers from the side closest to the furnace wall is used, and the furnace is estimated by extrapolation in the same way as the estimation of the furnace center gas temperature. What is necessary is just to estimate and estimate the gas temperature in a wall.

  Further, the furnace top gas average temperature can be measured with a thermometer installed in the furnace top gas riser.

  The reason why the central gas flow index is in the range of 2.0 to 3.0 is that if it is less than 2.0, the amount of gas to the center is insufficient, and sufficient air permeability in the furnace cannot be secured, or zinc gas is discharged. This is because there is an increased risk that the temperature of the furnace will be insufficient. On the other hand, if it exceeds 3.0, the high temperature gas is likely to damage the equipment at the top of the furnace. A preferred range for the central gas flow index is 2.2 to 3.0.

  Further, the peripheral gas flow index is set to a range of 1.0 to 1.5. If less than 1.0, the gas amount to the peripheral portion is insufficient, and ore existing in the peripheral portion of the furnace is gas reduced (indirect reduction). As a result, the rapid reduction (melting reduction) at the lower part of the furnace causes a deterioration in the air permeability at the lower part of the furnace, resulting in fluctuations in the blast pressure. This is because the stability of the operation is lost and the possibility of operation troubles such as hanging from the shelf and blowout increases, while if it exceeds 1.5, the amount of gas to the surroundings becomes excessive and the furnace wall This is because there is an increased possibility that the heat loss from the heat source becomes excessive and the reducing material ratio increases excessively. A preferred range for the peripheral gas flow index is 1.1 to 1.5.

  Then, the charge distribution control and / or adjustment of the wind speed before the tuyere may be performed so that both the central gas flow index and the peripheral gas flow index fall within the specified range at the same time.

  In this example, the charge distribution control is performed by appropriately operating the tilt angle and the number of turns of the turning chute (see, for example, Japanese Patent Laid-Open No. 11-117007, paragraph [0023]). The distribution can be adjusted freely. For example, if the O / C at the furnace center and the periphery of the furnace is reduced, the average O / C in the entire furnace radial direction needs to be kept constant, so that the O / C at the furnace intermediate part inevitably increases. Both the central gas flow index and the peripheral gas flow index increase.

  Moreover, the adjustment of the wind speed before the tuyere can be performed by changing the tuyere diameter and raising / lowering the blowing temperature. For example, if the wind speed before the tuyere is increased by reducing the tuyere diameter and / or increasing the blowing temperature, the central gas flow index is increased, and the peripheral gas flow index is decreased.

  Therefore, depending on the value of Bosch gas ratio (that is, the degree of production reduction), the central gas flow index and the peripheral gas flow index can be controlled by controlling the charge distribution and / or adjusting the wind speed before the tuyere. Both can fall within a predetermined range.

  It is recommended that the present invention be applied to blast furnace operation performed under high pulverized coal ratio operation conditions with a pulverized coal ratio of 150 kg / t-molten iron or higher. Under high pulverized coal ratio operating conditions, the coke ratio is small, and the average O / C in the furnace inevitably increases. Therefore, it is difficult to maintain good air permeability in the furnace even during normal operation. However, it is expected that maintenance of the air permeability in the furnace will become more difficult under the reduced production operation conditions. However, by applying the present invention, the air permeability in the furnace can be easily and reliably maintained. It is further recommended that the present invention be applied to blast furnace operation performed under high pulverized coal ratio operation conditions with a pulverized coal ratio of 160 kg / t-hot metal or higher, particularly 170 kg / t-hot metal or higher.

  In addition, it is recommended that the present invention be applied to blast furnace operation performed under pellet multiple blending operation conditions in which the pellet blending ratio in the ore is 15 mass% or more. When pellets are mixed in a large amount, the pellets are spherical, so they roll on the slope of the coke layer and flow into the center of the furnace, making it easy to block the central gas flow, so that the air permeability in the furnace is maintained well even during normal operation. However, it is expected that it will become more difficult to maintain the air permeability in the furnace under reduced production operation conditions. However, by applying the present invention, the air permeability in the furnace can be easily and reliably achieved. Can be maintained. It is further recommended that the present invention be applied to blast furnace operation performed under pellet multiple blending operation conditions with a pellet blending ratio of 30% by mass or more, particularly 50% by mass or more.

  In addition, the ore is usually mixed with pellets, sintered ore and / or block ore, and, if necessary, for the purpose of adjusting the basicity of blast furnace slag, contains flux component-containing substances such as limestone, silica, and converter slag. Although it mix | blends, the pellet compounding rate in an ore here is the value computed by making the total mass of only the ore seed | species except a flux component containing material into 100%.

(Modification)
In the above embodiment, an example in which the present invention is applied to the blast furnace operation of the bell-less charging method is shown, but when the present invention is applied to the blast furnace operation of the bell charging method, the angle of the armor plate and the displacement to the inside of the furnace By appropriately manipulating the amount, O / C distribution adjustment in the furnace radial direction, that is, charge distribution control can be performed (for example, JP 2006-131967 A, paragraphs [0017] to [0019]. reference).

In order to confirm the operational effects of the present invention, the present invention was applied when a significant reduction in production was performed in an actual blast furnace with an internal volume of 2112 m ³ (furnace port radius Ro = 3.9 m). The change was investigated.

The operating conditions, ore blending is assumed blended with limestone or the like at an external number at load ratio 70 percent by weight of the pellets, the furnace top pressure 1.7 kgf / cm ² [however a gauge pressure, 1kgf ^/ cm 2 = 98 .0665 kPa].

  The change of the operation result before and after applying the present invention is shown in FIG. In addition, the ventilation pressure fluctuation | variation in the figure is the value of the standard deviation calculated | required from the data of the ventilation pressure for 1 day measured every 1min.

Then, from the normal operation period [output ratio: about 2.0 t / (d · m ³ )] of the reference example shown in the figure, the production reduction operation period 1 of the comparative example [output ratio: about 1.4 t / ( d · m ³ )], the amount of oxygen enriched and the amount of air blown are reduced step by step to lower the output ratio and shift to operation under reduced production operating conditions. While maintaining the wind speed, an operation action was taken in which only the central flow was strengthened by reducing only the O / C at the center of the furnace.

  As a result, as shown in the figure, during the normal operation period of the reference example, the central gas flow index is in the range of 2.5 to 3.5, and the peripheral gas flow index is in the range of 1.2 to 1.5. Although the central gas flow index was maintained in the range of 2.5 to 3.0 in the production reduction operation period 1 of the comparative example, the peripheral gas flow index decreased to less than 1.0. However, the blast pressure fluctuation suddenly increased and reached 2.0 kPa or more, and the operation became unstable.

  For this reason, we tried to improve the air permeability in the furnace by reducing the pulverized coal ratio and increasing the coke ratio, but the recovery of the peripheral gas flow index to 1.0 or higher was not observed, and the blast pressure fluctuation remained large. Therefore, the improvement effect was not obtained.

Therefore, when shifting from the reduced production operation period 1 of the comparative example to the reduced production operation period 2 of the invention example, the output ratio remains fixed at about 1.4 t / (d · m ³ ) and the O / C at the center of the furnace. Was maintained and the O / C in the middle part of the furnace was raised to lower the O / C in the peripheral part of the furnace, and as shown in the example of the invention, the central gas flow index was While maintaining the range of 2.0 to 3.0, the peripheral gas flow index is restored to the range of 1.0 to 1.5, and the blast pressure fluctuation is less than 2.0 kPa, which is the same as the normal operation period of the reference example. The operation was stabilized. Therefore, in the production cut-off period 2 of the invention example, the coke ratio is gradually lowered while maintaining the reducing agent ratio substantially constant while keeping the output ratio fixed at about 1.4 t / (d · m ³ ). Although the pulverized coal ratio was gradually increased to increase the pulverized coal ratio to about 200 kg / t-hot metal exceeding the pulverized coal ratio of about 180 kg / t-hot metal in the normal operation period of the reference example, the central gas flow index was 2. In the range of 0 to 3.0, the surrounding gas flow index is also secured to 1.0 to 1.5, and the blast pressure fluctuation is maintained at a low value comparable to the normal operation period of the reference example, and the high pulverized coal ratio It was confirmed that the air permeability in the furnace was ensured even during operation and stable operation could be realized.

  FIGS. 2 to 4 show the above-described operational process again by rearranging the relationship between the Bosch gas ratio, the central gas flow index and the peripheral gas flow index, and the relationship between the Bosch gas ratio and the variation in the blowing pressure.

Here, in FIG. 2, the Bosch gas ratio is about 1.8 Nm ³ / (min · m ³ ) and the central gas flow index shows the minimum value. This is due to the following reason. That is, when the Bosch gas ratio is lowered from about 2.0 Nm ³ / (min · m ³ ) to about 1.8 Nm ³ / (min · m ³ ), the operation action for strengthening the central flow has not yet been taken. Therefore, as the Bosch gas ratio decreases, the amount of gas toward the furnace center decreases, the furnace top center gas temperature decreases, and the center gas flow index decreases, whereas the Bosch gas ratio decreases by about 1. When further lowering than 8 Nm ³ / (min · m ³ ), the operation action was taken to reduce the O / C at the furnace center and strengthen the central flow. This is because the gas amount toward the furnace center increases, the furnace center gas temperature rises, and the center gas flow index rises.

  On the other hand, in FIG. 3, the peripheral gas flow index decreases as the Bosch gas amount decreases between the reference example and the comparative example, and the peripheral gas flow index increases between the comparative example and the invention example. This is because, for the first time between the comparative example and the invention example, the operation action for enhancing the peripheral flow was taken.

  Although already demonstrated using the operation transition diagram of FIG. 1, although it is clear also from FIGS. 2-4, in the period of a comparative example, although a center gas flow index exists in the range of 2.5-3.5, The gas flow index is less than 1.0, and the blast pressure fluctuation is as large as 2.0 kPa or more, whereas in the period of the invention example, the central gas flow index is in the range of 2.0 to 3.0, and the surroundings It can be seen that the gas flow index is in the range of 1.0 to 1.5 and the blast pressure fluctuation is maintained below 2.0 kPa.

Claims (3)

A method for operating a blast furnace under a reduced production operating condition in which a Bosch gas ratio defined by an amount of Bosch gas per 1 m ^{3 of a} blast furnace volume is 1.8 Nm ³ / (min · m ³ ) or less,
While the central gas flow index defined by the furnace top gas temperature (° C.) / Top gas average temperature (° C.) is 2.0 to 3.0,
Charge distribution control and / or pre-tuyere wind speed so that the ambient gas flow index defined by the furnace top ambient gas temperature (° C) / top gas average temperature (° C) is 1.0 to 1.5. A method of operating a blast furnace, characterized by adjusting.   The blast furnace operating method according to claim 1, which is performed under a high pulverized coal ratio operating condition with a pulverized coal ratio of 150 kg / t-molten iron or higher.   The blast furnace operating method according to claim 1 or 2, wherein the pellet mixing ratio in the ore is carried out under pellet multiple mixing operation conditions of 15 mass% or more.

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